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Saturday, 18 June 2016

Promotion. An Expected Goals Perfect Storm.

Although most fans will have their attention focused firmly on Euro 2016, mid June is also an exciting time for followers of the promoted teams with the gradual release of the new season fixtures.

The greatest anticipation will be felt, along with a certain trepidation, among the supporters of Middlesbrough, Burnley and Hull, who reacquaint themselves with the newly enriched Premier League.

Promotion to the top tier no longer automatically offers short term monetary gain in exchange for regular defeats and a swift return to the Championship. But the regular success supporters became accustomed to in their promotion season will not be repeated in 2016/17.

The stark reality for promoted teams is that they will score fewer goals and concede more than they did in the Championship and most would happily take 17th spot come May 2017 and a chance to grow into their newfound affluent position.

A team scores goals through shot volume, shot quality, taking shots from better positions and then having players that can finish these opportunities consistently well.

These factors can be followed with increasing difficulty.

Volume merely involves counting, this is followed by an expected goals based model and finally a repeatable over performance in such a model that is unlikely to be wholly down to random variation.

The three promoted teams to the Premier League in 2015/16, Bournemouth, Watford and the subsequently relegated Norwich mustered nearly 2,200 non penalty goal attempts between themselves in their promotion year, but this fell to just 1313 during their Premier League campaigns.

Accounting for the greater number of Championship games, the rate per game fell from just under 16 to 11.5. Attempts allowed increased from 11.5 to 12.5 in the Premier League.

However, proportionally, goals scored and allowed fell and rose by larger amounts.

Goals scored by the promoted three fell by 45% in the next Premier League season compared to just a 27% fall for attempts and goals conceded increased by 55% compared to just a 5% increase for attempts allowed.

So based on the experience of last season there appears to be a disconnect between the change in goals scored when going from the Championship to Premier League and the change in attempts.

One possible cause for this disproportionately large change in actual goals across the two seasons is that promoted teams, as well as experiencing a change in shot volumes, will also find chances they both create and face will be converted at different rates in Premier League compared to the Championship.

Around 13% of the games the promoted trio played in the Championship was against sides who then fell into the third tier of Division One, while over 20% of their subsequent Premier League games would be against teams competing in the Champions League.

So it is fair to assume that the overall quality of opposition will rise sharply.

We may see if this is a reasonable assumption by adding a term to a shot model to distinguish between attempts made in the two different leagues for the three promoted sides to see if there is a significant difference in success rate when taking a shot in the Premier League and an identical one based on shot location in the Championship.

Based on the experience of Bournemouth, Watford and Norwich, the Championship was an easier place for them to convert similar chances than was the top flight.

Attempts from the same pitch location were less likely to result in a goal in the Premier League, more likely to be off target and more likely to be blocked compared to the Championship.

As an example, a shot from the edge of the box in the Premier League was converted 5% more often by the promoted trio in the Championship compared to identical efforts in the Premier League.

It is easy to surmise a range of contributing factors.

The level of opposition talent faced by these nascent Premier League sides in their promotion year on average was likely to be well below that faced subsequently.

This not only includes the level of goalkeeping talent, but also the ability of Championship sides to defend as a unit, close down potential assists and disrupt the creation of clear cut opportunities.

Although the promoted teams may be capable of creating chances, the level of defensive pressure during the shot may be significantly greater in the Premier League.

In short, the competitive environment faced by the promoted teams inevitably shifts upwards.

This reduced likelihood of converting chances compared to the experience in the lower grade of the Championship is repeated on the defensive side of the ball.

When faced with Premier League quality attacking, attempts conceded from identical pitch positions are less likely to be blocked than in the previous campaign, more likely to require a save and more likely to concede a score,

So if the most recent batch of promoted teams are typical, supporters of 2016/17's newly arrived trio can expect fewer attempts, with a reduced likelihood of scoring compared to comparable opportunities in the Championship and a similarly rough deal in defence.

Making survival, if they can emulate Watford and Bournemouth, all the more sweet come May 2017.